The invention relates to a hydrocarbon conversion process in which carboxylic acids or esters are produced by reaction of carbon monoxide and water or an alcohol with a hydrocarbon chain substrate such as an olefinic hydrocarbon. More specifically, the invention relates to a multi-step process for the production of carboxylic acids from straight or branched long chain paraffins by sequential dehydrogenation and carbonylation.
The production of carboxylic acids by the carbonylation of the corresponding olefin is a well described in the art and is also practiced commercially, although primary for the production of low molecular weight acids such as acetic acid.
The use of a palladium based carbonylation catalyst is described in a paper at page 3192 of J. Org. Chem., Vol. 38, No. 18, 1973 by D. M. Fenton. This reference describes the effects of a number of variables including temperature, additional reagents, solvents, and the identity of the phosphine substituents of the palladium-phosphine complex used as the catalyst. A similar paper by J. F. Knifton at page 2885 of J Org. Chem., Vol. 41, No. 17, 1976 describes the production of carboxylic acid esters from linear xcex1 olefins using a ligand-stabilized platinum(II)-group 4B metal halide catalyst exemplified by [(C6H5)3P]2PdCl2xe2x80x94SnCl2. This reference reports the result of using a variety of palladium complexes and reported the performance of the catalyst system varied with the coordinated ligands. The reference also indicates that internal, disubstituted olefins carbonylate more slowly than linear olefins and produce a different product distribution.
Another interesting reference is the Hoffman et. al. paper (Ind. Eng Chem. Prod. Res. Dev., 1980, 19, 330-334) which describes the examination of 300 combinations of nonnoble group 8 metals and halogen-free promoters as catalysts for carbonylation. An apparent optimum catalyst system of cobalt/pyridine or xcex3-picoline and xcex1octene was used to study the affects of various parameters on the carbonylation of a mixture of isomeric internal n-dodecenes. This reference describes the usage of hydroformylation to produce fatty acids and xe2x80x9cfatty typexe2x80x9d alcohols and indicated carbonylation had not yet been used to produce fatty acid esters or alcohols commercially. The reference includes, as FIG. 8, a suggested process flow for the recovery of the product acid esters of a carbonylation process.
U.S. Pat. No. 4,960,926 issued to E. Drent describes another catalyst system for carbonylation comprising a homogeneous palladium catalyst, an organic phosphine, a non-carboxylic or non-halogen acid of set character, a promoter and a catalyst stabilizer. The reference indicates the unsaturated compounds in the feed stream which are converted in the reaction can be cycloalkenes. A paper by E. Drent, et al published at pages 247-253 of the Journal of Organometallic Chemistry, 455 (1993) describes the effects of different ligand structures and acid types in what appears to be a similar catalyst system.
U.S. Pat. No. 5,254,720 issued to T. Wu describes a process for producing aliphatic carboxylic acids or their alkyl esters using a catalyst system comprising palladium and copper compounds, at least one acid stable ligand, and an acid such as hydrochloric acid. This reference also indicates an optional solvent may be present in the reaction zone and lists as possible solvents a variety of ketones including acetone and aromatic hydrocarbons including xylenes. U.S. Pat. No. 5,869,738 issued to L. R. Pan et al. describes another carbonylation catalyst system comprising a Group VIII metal such as palladium or palladium chloride supported on a carrier, a ligand such as triphenylphosphine and an acid such as an alkyl sulfonic acid. The reaction may be carried out in an inert organic solvent. Mentioned solvents include an aliphatic hydrocarbon e.g. octane, an aromatic hydrocarbon such as benzene or a halogenated hydrocarbon such as chloroform or a mixture of these.
The use of nitrogen-containing heterocyclic compounds as a carbonylation catalyst component is known in the art. For instance, U.S. Pat. No. 5,866,716 issued to M. Schafer et al. describes a catalyst system based upon a halogen-free rhodium compound and a nitrogen-containing heterocyclic compound such as pyridine, quinoline or imidazole.
U.S. Pat. No. 5,981,796 issued to A. J. M. Breed, et al, describes a process for the manufacture of what are characterized as trialkylacetic acids having from 5 to 19 carbon atoms per molecule by the reaction of a branched olefin with carbon monoxide and water in the presence of a heterogeneous catalyst. The use of a resin type catalyst having sulfonic groups is preferred, but the use of a zeolitic catalyst is also referred to. The reference indicates the process can be practiced in a continuously backmixed reactor such as a stirred tank rector (CSTR), fluidized reactor or recycle reactor.
It is known in the art of catalytic reforming to contact the feed stream fed to a pilot plant with sodium in order to remove sulfur from the feed stream.
The invention is a continuous process for the conversion of long chain aliphatic paraffins to oxygenate hydrocarbons such as organic acids and alcohols via carbonylation (hydrocarboxymethylation). The invention also includes a unique carbonylation method which employs a multicomponent homogeneous catalyst system.
The invention may be characterized as a continuous process for the production of oxygenated hydrocarbons which comprises passing a feed stream comprising at least two different paraffinic hydrocarbons, each having a carbon number above 6, into a dehydrogenation zone operated at dehydrogenation conditions and converting a least a portion of the entering paraffinic hydrocarbons to olefinic hydrocarbons of the same carbon number to form a dehydrogenation zone effluent stream comprising a mixture of olefinic and paraffinic hydrocarbons; passing at least a portion of the hydrocarbons of said dehydrogenation zone effluent stream, carbon monoxide and a nucleophile supplying feed, preferably a hydroxyl-supplying feed compound chosen from water and a light alcohol, into contact with a homogeneous carbonylation catalyst in a carbonylation zone operated at carbonylation conditions and converting at least a portion of said olefinic hydrocarbons to desired carbonylation products, and recovering a product stream comprising carbonylation products and paraffinic hydrocarbons from the carbonylation zone; passing said product stream into a fractional distillation zone in which the product stream is separated into at least a hydrocarbon recycle stream comprising paraffinic hydrocarbons and an oxygenate stream comprising carbonylation products; recycling the hydrocarbon recycle stream to the dehydrogenation zone; recovering the carbonylation products.
Another embodiment of the invention may be characterized as a carbonylation process which comprises passing water, carbon monoxide and a C8-plus aliphatic substrate having a carbonylizable double bond, such as an alkene, ester or alcohol into a carbonylation reaction zone maintained at carbonylation conditions and into contact with a homogeneous carbonylation catalyst system comprising either palladium and imidazole or a Pd (PPh3)2 complex, an aliphatic organic acid and a solvent to produce corresponding carboxylic acids, and recovering said carboxylic acids from the carbonylation reaction zone.
The subject process is capable of achieving greater than 95% conversion of a long chain olefin, such as 1-dodecene at greater than 95% selectivity to a carboxylic acid which contains at least 50% linear products (1-tridecanoic acid).